Guinea pig inclusion conjunctivitis agent, a member of the genus Chlamydia, causes an infection of the vagina and male urethra and is sexually transmitted among guinea pigs. Male to female transmission of this chlamydial infection has been demonstrated elsewhere (by Professor A. Barron) and in this laboratory and experiments are currently underway to show female to male transmission. The infectious dose for females and males has been determined and the number of infectious doses present in the genital tract at various times during the infection will be estimated. Female and male guinea pigs have been infected in the genital tract and after recovery were challenged to test for immunity. Previously infected females and males, which were immune to rechallenge, are tested for serum antibody, secretory antibody in genital secretions, and cellmediated immunity. The effect of chlamydial infection in the vagina on the fertilization and abortion rates of mated females is being assessed. These rates are being compared to those of females which are immune and are similarly challenged. In further experiments of resistance to reinfection, females will be vaccinated systemically and topically in the vagina, while males will be vaccinated systemically prior to standardized challenge. Antibiotic treatment of infected females will be attempted by systemic injection and by application of antibiotic-containing inserts in the vagina.